Human Ancestors' Earliest Tools Found in Africa

By JOHN NOBLE WILFORD

Published: April 25, 1995

STONE tools found in the desiccated fossil fields of Ethiopia have been dated at 2.6 million years old, making them the earliest known artifacts created by humans or their direct ancestors.

Simple cobbles fractured and flaked for use in scraping and cutting, the tools were made and gripped by hands apparently well evolved toward the hands of humans and conceived by minds somewhat less far along the evolutionary path. These were toolmakers, though, probably adjusting to new environmental conditions, a cooler climate and changing vegetation, by trying out new means of getting and processing food. Whoever they were, whatever their needs, they certainly were innovators back near the beginning of the human experience.

The discoveries provided strong evidence that toolmaking, once thought to be a skill special to the Homo genus, began long before its emergence, perhaps by half a million years. Fossils of the early human ancestors themselves have yet to be identified in the tool-bearing sediments of the Ethiopian site. But the scientists reporting the new data said it was a reasonable assumption that the tools could have been made by more primitive members of the human lineage, the australopithecenes, the only hominids known to have existed at that time.

The existence of some early stone tools in the ground near the Gona River had been known since the 1970's. Preliminary analysis indicated that they were probably much older than any previously discovered artifacts, but nothing was firm. When new explorations in the Gona region over the last three years uncovered thousands of these crude tools, more precise geological dating tests were conducted.

Sileshi Semaw, an Ethiopian archeologist who is a doctoral student at Rutgers University in New Brunswick, N.J., announced the test results at a recent meeting of the American Association of Physical Anthropology in Oakland, Calif. Argon isotopic analysis and other evidence, he reported, showed ages of 2.5 million to 2.6 million years for the sediments where the tools were found, with the true date probably being closer to the greater age.

In that case, Mr. Semaw concluded, this collection of artifacts is the oldest known in Africa and thus the world. Tools discovered at Olduvai Gorge in Tanzania by Louis and Mary Leakey, the famous husband-and-wife team of fossil hunters, are about two million years old, and other recent finds in Kenya and Ethiopia have been determined to be several hundred thousand years older, but not as ancient as the Gona artifacts.

Other archeologists and paleontologists agreed that the findings were an important step in the study of human origins, especially in the poorly understood period from three million to two million years ago. Dr. Ian Tattersall, a paleoanthropologist at the American Museum of Natural History in New York and author of "The Fossil Trail," published recently by Oxford University Press, said, "The new set of dates certainly firm up dates for very early toolmaking, and that's certainly a significant finding."

But at the scientific conference, the stone tools of Gona were overshadowed by rancorous charges and countercharges touched off by Mr. Semaw's accusations of "a violation of professional ethics" by another research group that he said had invaded his site last October. The group, from the Institute of Human Origins in Berkeley, Calif., headed by Dr. Donald C. Johanson, discoverer of the celebrated Lucy fossils, flatly denied the allegations.

The tempest has yet to subside, however, as scientists in the often contentious field of paleoanthropology are taking sides and airing bitter complaints about claim-jumping.

Dr. J. W. K. Harris, who has explored the Ethiopian fossil beds for years and is now chairman of the Rutgers anthropology department, was among the first to find tools in the Gona region, where he discovered a few scattered samples in 1976 and 1977. Beginning in 1992, he and Mr. Semaw conducted the first systematic surveys there, identifying 21 sites containing thousands of stone tools and ancient animal remains. Most of the tools were stone pebbles, usually of lava, that had been struck repeatedly with a second pebble as a hammer. This produced a crude chopper or scraper, as well as numerous sharp flakes for cutting.

Dr. Craig Feibel, a Rutgers geologist, collected samples of volcanic ash for use in dating the material. Then Dr. Paul R. Renne, president of the Berkeley Geochronology Center in California, ran tests with a recently perfected geological dating technology known as argon-argon single crystal laser fusion. He has also applied the technology in dating the crater in the Yucatan peninsula of Mexico that is implicated in the asteroid collisions that may have wiped out the dinosaurs. Previous techniques required much larger samples than are usually available.

"It's the most precise, most broadly applicable test out there in archeology and geology," Dr. Renne said.

The analysis produced a date of 2.517 million years, with only a slight margin of error. Because the dated ash lay just above the 15-foot-thick tool sediments, Dr. Renne said, the tools are assumed to be somewhat older. By how much? Rock found below the sediment held the record of a previously dated reversal of earth's magnetic field. The date for that is about 2.6 million years ago, and the artifacts appeared to be much closer to that boundary than to the volcanic ash that is overlying the sediments.